The amount of generated electrical power of a wind power electric generator largely varies with a wind speed. Thus, the wind power electric generator is installed at a place where a large yearly average wind speed is obtained, but is largely affected by a daily weather state because appropriate wind is not always obtained. For this reason, when a rotating electric machine is used as the wind power electric generator, it is difficult to predict change of a rotational speed and a repetition frequency as compared to a case in which any other rotating electric machine is used, a rotor as a rotating unit is potentially fatigued due to repetition of application of stress by a centrifugal force. Typically, the lifetime of a material is determined by the magnitude of the stress and the number of repetition of the application. Since the number of repetition of application of the stress depends on a wind condition, the magnitude of the stress applied on the rotor needs to be reduced to achieve a longer lifetime.
The material of the rotor is mostly iron (iron core) and copper (coil), and the coil is provided in the iron core. This part is covered by iron having a strength higher than that of copper, and thus has a sufficient strength. However, each coil outside of the iron core is connected by a neutral ring (made of, for example, a copper material), and no member is provided to achieve strength enhancement. Thus, a longer lifetime can be achieved by reducing stress in a structure in which the neutral ring and the coil are connected with each other.
Examples of technologies related to the neutral ring include those disclosed in Patent Literatures 1 or 2. In Patent Literature 1, the neutral ring is installed in a ring rigid body supported by and fixed to a rotor end plate supporting the rotor iron core at a peripheral part. In Patent Literature 2, the neutral ring is embedded in and supported by a support of a rotor coil.